Preparation of a biological sample that is imaged in a TEM can be a complex procedure. Biological specimens (or samples) for use in a TEM are thin compared with specimens that are imaged using other types of microscopes such as optical microscopes. For a TEM, the specimen to be imaged should be of thin enough to allow electrons to travel through the specimen. The sample is prepared by cutting a very thin slice (section) from a sample embedded within a sample block, which can be made of plastic that infiltrates and surrounds the biological sample, polymerizes into a solid plastic block. The block is cut into thin sections by a blade using the microtome, which automates the process. Each section can be 20 nanometers (nm) to 2 micrometers (μm) thick.
Thin sectioning of samples suspended in sample blocks using an ultramicrotome is typically done by a highly skilled human operator. The level of skill, and the degree of effort to perform such sectioning without cutting errors can present challenges to sectioning volumes that are large enough to provide a complete understanding of the fine structure of organisms that are more complicated than small analids (worms).